This could probably be done more elegantly...
In my crontab:
0 * * * * if [ `wget -q -O - http://www.weather.gov/xml/current_obs/KCMX.xml | xpath "/current_observation/temp_f/text()" 2>/dev/null | xargs printf "%1.0f"` -gt 70 ]; then /usr/local/bin/heyu fon B1; fi 10 * * * * /usr/local/bin/heyu foff B1
Basically, if it's greater than 70° F outside, turn on the X10 circuit for my upstairs fan and run for 10 minutes each hour. I give myself bonus points for including XML (which makes it an Enterprise Solution).
